For me, there's nothing stopping females from being important in the Imperial structure at all. I believe there's at least 1 canonical female Moff, and of course Mara Jade. My Stormtroopers are around 60% clone during the Rebellion Era, just cause that's a number I remember finding on some basic research I did when I determined I was going to run a game. It's more of a numbers thing than anything else.

In terms of alien representation, I assume a few different things.

1. The more core world you are, the more likely you are to find racist Imperials. It just seems entirely unlikely that on places with tenuous control as is, the Empire would be able to be nearly as functionally racist as it could where the bulk of it's resources are being directed.

2. The Core World Imperials are a lot like the Hutts. Functionally racist, until proven otherwise. Bothans, Falleen, Chiss, and a number of other races have clearly proven themselves as capable, and thus have earned their place.

3. It's a lot harder to think of the Empire for me as this massive racist body. First, you had the Galactic Senate, which was comprised of aliens dictating policy when the Emperor and Moffs weren't. Then you have all of Clone Wars to wedge into there, where Republic, clones and all, are working closely with all kinds of different races. That's a lot of massive systemic racism to accept from the bulk of the galaxy in only 20 years time.

4. In my games I assume the galaxy is full of both good and bad people. Not every Imperial is going to be a monster. Not every Rebel is going to be a saint. In particular, I assume that there are plenty of bad people who fell in with the Rebellion due to their hate of the Empire. It certainly seems like it's a time where beggars can't be choosers, and there are likely terrorist organizations that found working with the Rebellion to be an easy way to work toward their goals with a much larger support group.

I accidentally ruined my first Edge campaign's PC group from joining the Rebellion in this very manner, which really cemented it home for me. The party drunkenly outted their Rebel contact as a known terrorist known for a few successful bombings after a successful Underworld check revealing that info to them. With the PCs drunkenly blabbing this info all over, the Rebel tried to clean house, so to speak.

Not every criminal the Empire is hunting doesn't deserve it, and there would certainly be plenty of Imperials who believe in the sanctity of the law, or in protecting their community. Lot's of idealist Core Worlders likely sign up for the Imperial Academies, and on massive metropolitan planets, why would there not be aliens who've grown up under the umbrella of the Empire who feel loyal and patriotic towards it.